Questions on refining gold from rich ore with HNO3 + HCl

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Anonymous

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I recently found some interesting meta-sedimentary rocks in a nearby stream that runs through my property, which contain a healthy mixture of metal chunks and veins. Some of the stones have chunks of metal large enough that a few small dull yellow/black metallic "domes" are present on rounded surfaces (seemingly from malleable metal rolling down the stream bed).

I got excited and picked up a small bottle (about 10mL). of HNO3 + HCl solution from a friend who had an 18K gold testing kit. I know the solution is supposed to go bad over time, but this mixture seems to be pretty stable...no apparent pressure in the bottle, and it's never been opened it since he bought it (a few months back). Furthermore, the acid is very effective at dissolving pretty much everything but the quartzite and other silicates from the multicored rock (about 70% Silicate 30% Metal).

For what it's worth, I did some scratch testing and such before crushing/dissolving, and there seemed to be just as much
brittle iron ore and pyrite as there was malleable metal in the diverse rock...including small amounts of copper and lead

Last night, I carefully contained and partially crushed the rock, and dissolved about 0.2kg in all 10ml of acid in a 6" wide pyrex dish. I left it overnight on a warm ceramic tile near my wood stove air intake, and added some water this morning. I came home from work this evening, and I now have a relatively thick faintly brown/yellow solution, which contains:

- Countless small golden flakes/plates
- A pile of rusty orange "mud" covering the bottom of the dish
- A few crusty black chunks that I can crush by carefully prodding (which then dissolve almost instantly)
- 5 ~2-3mm diameter heavy black metallic chunks, which seem to be pretty solid and not malleable.

I then removed all the leftover fragments of quartzite, sand, and mica with tweezers. What was interesting to me is that there were many more golden flakes in the dish this mornig than when I set it down last night...and when I added a drop of water this eve (with a few crystals of Baking Soda dissolved in it), a couple more tiny flakes seemed to precipitate out of the solution.

Fear not, no need for the safety lecture here :) ... I am a degreed and enthusiastic scientist, not in chemistry, but I've aced (and enjoyed!) enough chemistry classes/labs in college to understand the basic reaction processes and safety precautions when dealing with caustic liquids and dangerous fumes.

I just want some advice on what steps to take next....

1) How should I refine/purify any metals (particularly gold) that may be present both in both flakes/plates and within the solution?

2) What material should I use to filter the flakes? I fear the solution will disintegrate a coffee filter, and I don't want to make a mess. The acid doesn't seem to bother plastic much, but not sure where to get a plastic filter...and I don't want to neutralize the acid until after filtering out the flakes, which have an impressive luster!

3) Once filtered, Is there anything "household" that I can use to carefully adjust PH and precipitate any aqueous gold that may be present? I do not want to spend any money on chemicals/supplies until I know for sure that the material is of at least some value.

Just trying to get some purified specimens so that I can identify the content of any valuable metals present in the rock. Any advice would be much appreciated! Thank you.

Thanks

BC
 

butcher

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Ore treating with acids, without pretreatment would not yield much if any results.

If I had some ore and I wanted to know if they contained values:
Crush and classify, concentrated by gravity, crush to fine powder, roast slowly at first then bring to red, in air > 900 deg C if sulfides Iron added, now smelting with litharge and flux (depending on ore type oxidizing or reducing), to get lead button containing values, then this is cupel this to rid lead, smash and part button, now the metals can be determined, with acids.

Easier method, concentrate by gravity, send concentrates to have them assayed.
 

manorman

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If you have much of this material it would be a great idea to have an assay done to know if it's worth while. They do not cost much and save you a ton of wasted time.
 

orvi

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assay, assay, assay... treating gold ore with acid is one of the worst methods to determine the presence of gold, not to mention that determining the content of gold. if it was that simple, every assay lab in the world would do that way.
best results are obtained with fire assay (mentioned above), very good results are given with just panning (if gold is visible) and smelting the roasted concentrates with some kind of oxidating flux. metal button is produced, which can be directly assayed with XRF (professionals) or IN THIS STEP dissolved with aqua regia (if there isnt big silver content) and tested for presence of gold (eg stannous chloride solution).
i recommend crush the ore and send it directly for fire assay, or get it zapped with X-ray.
 

Reno Chris

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If you look historically at old posts, there are probably more than 100 previous posts about how to treat gold ore with Aqua Regia - and the answer is always the same. DON'T DO IT! It does not work. Lots of things (like sulfide minerals) can contaminate your acids and consume them before they can get to dissolving the gold (if there is any). I have many folks ask about their gold ore finds from my Youtube channel and its almost always the same - unless they are well experienced, the percentage of people who think they have made a big discovery but are wrong is very nearly 100%.
So get an assay test done by a competent professional lab to see what you really have. Until the lab assures you that you have good quality gold ore, dont even bother to think about the chemistry of how to treat your ore.
What is quality ore? I would say at a bare minimum of 10 ppm, much better in the range of 20 or 30 ppm. 10 ppm is roughly 1/3rd of a troy ounce per ton of rock. If you want to see a video about how I extracted the gold from moderately rich gold ore and made a button from the gold, I did this YouTube video on the topic: https://youtu.be/rJqFxu0Wko0
 
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butcher

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Reno Chris,

Great to see you still hanging out here on the forum, your advice and help as a professional gold miner are always welcome, and lucky for us, you also know the refining side as well.
 
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